I have an extra tensioner positioned low above the ground, running with a pulley wheel intended for a recumbent, that came with well sealed steel bearings. After about a year of riding the bearings would rust through and seize. I solved the problem by going with ceramic bearings.

Engineering-wise those bearings are fantastic, just a marvel. You are astounded when you rotate them. Their potential negative might be the catastrophic failure mode. In my application they do not carry much load, so I cannot tell about that.

The cost difference is of little issue after you have changed the seized bearings for the third time, each time engaging in a tedious dismantling and reassembling of the setup.